In the present paper we propose a doubly orbitally degenerate narrow-band model with correlated hopping. The peculiarity of the model is taking into account the matrix element of electron-electron interaction which describes intersite hoppings of electrons. In particular, this leads to the concentration dependence of the effective hopping integral. The cases of the strong and weak Hund's coupling are considered. By means of a generalized mean-field approximation the single-particle Green function and quasiparticle energy spectrum are calculated. Metal-insulator transition is studied in the model at different integer values of the electron concentration. With the help of the obtained energy spectrum we find energy gap width and criteria of metal-insulator transition.
A microscopical model of doped fulleride electronic subsystem taking the triple orbital degeneracy of energy states into account is considered within the configurational-operator approach. Using the Green function method, the energy spectrum at the integer band filling n = 1 corresponding to AC60 compounds is calculated. A possible correlation-driven metal-insulator transition within the model is discussed.
The model of a strongly correlated system in which periodically spaced AndersonHubbard centers are introduced into narrow-band metal is considered. Besides the interactions between localized magnetic moments and strong on-site Coulomb interaction, the model takes into account the hybridization of localized and band states. To study the eect of the lattice deformation on the electrical properties of the system, the phonon term and elastic energy have been taken into account. Green functions for band and localized electrons have been found. On this base, the energy spectrum has been investigated as a function of model parameters, temperature and external pressure. The criterion of the metalinsulator transition for an integer value of electron concentration has been derived and the phase diagram of the metalinsulator transition has been built.
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